Work continues on the purification of SV40 t Antigen from clones of E. Coli transformed by suitable plasmids carrying a strong lac promoter and a hybrid ibosome binding site immediately upstream of a cloned SV40 t cistron. Attempts are also underway to isolate a rich animal cell source of the protein. The goal of the work is to isolate purified, biologically active t and to evaluate its biochemical role in the process of SV40 induced neoplastic transformation.